I know many don't recommend it, but can you give a half dose of melafix and black out his tank for a few days? If you have Indian almond leaves, maybe put a large fresh one in for him. Do a 50% water change first, and then give him melafix or a multicure if you have any on hand. I've got no good advice, I'm sorry. I had a similar experience with Flash, but it wasn't a good outcome.
I'm sorry hon. I hope he picks up soon.
a) growth on tongue is not old age
b) with how fast the "growth" is growing, I'm guessing it's an internal bacterial infection. Adding Garlic and Vitamins to the water and adding about 1/8th dose aquarium salt could be a good idea. unfortunately, IME anti-bacterial meds added to water do little for internal infections, but you could try it anyways.
some fish have tongues called basihyal or something like that, there is even a fish tongue parasite that attaches itself to a snapper's tongue, sucking the blood out of the tongue, causing it to atrophy and then it replaces the fish's tongue and acts like a tongue. gross and neat at the same time.